In recent years, flat display panels such as liquid crystal panels and plasma display panels are increasingly used as display elements for image display devices such as television receivers instead of conventional cathode-ray tube displays, allowing image display devices to be made thinner. Liquid crystal panels used in liquid crystal display devices do not emit light on their own, and therefore, it is necessary to provide a separate backlight device as an illumination device. The backlight device is disposed on a rear surface of a display panel opposite to the display surface, and includes a light source, a light guide plate that converts light from the light source to light to illuminate the screen, and a metal chassis that stores these components therein, for example. The backlight devices are generally categorized into a direct-light type and an edge-light type, and between the two, the edge-light type has a greater advantage than the direct-light type in terms of making the device thinner.
In the edge-light type backlight device, the light guide plate has a light-emitting surface facing the display panel, and a light-receiving surface on a side face thereof, and the light source is disposed facing the light-receiving surface. An LED is suitably used as the light source, but in order to use LEDs for the edge-light type, it is necessary to arrange LEDs at a high density so as to obtain a required light amount. This causes an increase in temperature around the LEDs, resulting in problems such as a reduction in light-emitting efficiency of LEDs and a heat deterioration of LEDs. As a technique to solve the above-mentioned problems, the configuration disclosed in Patent Document 1 is known.
The backlight device described in Patent Document 1 includes: a plurality of light guide plates arranged in a tandem manner; LED substrates having an L-shaped cross section and having LEDs mounted thereon so as to correspond to the respective light guide plates; heat-dissipating plates having an L-shaped cross section and bonded to opposite surfaces of the respective LED substrates to the LED mounting surfaces; a sub-chassis that defines the positions of the LED substrates and the light guide plates to each other; and a rear frame to which these components are attached. With this configuration, each contact area between the LED substrate and the heat-dissipating plate, and between the LED substrate and the sub-chassis can be made larger, and a heat-transfer resistance between the respective members can be made smaller. As a result, it is possible to improve the heat-dissipating efficiency in dissipating heat from the LEDs to the outside through the rear frame.